1. Field of the Invention
The present invention relates generally to discharge lamps, and more particularly, to a discharge lamp for use in tanning applications, wherein the lamp includes a vitreous tube having a series of grooves formed in its periphery.
2. Background of the Related Art
Discharge lamps have been in existence for many decades. Discharge lamps consist primarily of an elongated vitreous tube having axially opposed end seals and coated on the inside with phosphor powders which fluoresce when excited by ultraviolet light. Filament electrodes are mounted on the end seals of the tube and are connected to base pins which engage with the lamp housing. The elongated tube is filled with a rare gas, such as argon, and a drop of mercury.
Discharge lamps typically operate at a relatively low pressure. In operation, an alternating current is applied to the electrodes which increases the electrode temperature and causes the emission of electrons therefrom. These electrons are accelerated by the voltage across the tube until they collide with the mercury atoms, causing them to be ionized and excited. When the mercury atoms return to their normal state, mercury spectral lines in both the visible and ultraviolet region are generated. The ultraviolet radiation excites the phosphor coating to luminance. The resulting output is not only much higher than that obtained from the mercury lines alone, but also results in a continuous spectrum with colors dependent upon the phosphors used.
Typically, the intensity of the ultraviolet radiation emitted from the discharge lamp differs along the length of the lamp, but does not vary dramatically nor are distinct regions of varying intensity created. In applications such as tanning, which will be discussed in more detail supra, it would be advantageous to have distinct regions of ultraviolet radiation intensity.
Since the late 1970s, the practice of tanning, defined as the darkening of one's skin through exposure to ultraviolet (UV) radiation, has increased in popularity in the United States. Each person's skin reacts differently to UV radiation exposure, with the reaction being dependent upon genetically determined factors, such as the amount of melanin pigment already in the skin naturally and the capability of the person's skin to produce additional melanin (facultative pigmentation).
Melanin is the dark pigment found in the retina, hair and skin, except for the palms of the hands, soles of the feet and lips. Without the protection afforded by the melanin pigment, a person's skin would burn when exposed to UV radiation. As stated above, the skin includes naturally occurring melanin pigment and produces additional melanin. Melanin is produced by special cells called melanocytes, which are located deep within the outer layer of the skin. When the melanocytes are stimulated by ultraviolet light, they utilize an amino acid called tyrosine to produce the pigment melanin. Since the melanin pigment is only able to absorb ultraviolet light of approximately 260-320 nanometers, UVB radiation is needed to achieve melanin production. UVA radiation which has a wavelength of approximately 320-400 nanometers can formulate melanin, but only when there is enough photosensitizing material already in the skin to trigger a UVB reaction. With the presence of UVB, melanocytes are stimulated to divide, creating more pigment cells. During this time, the epidermis thickens to form additional protection, a condition referred to as acanthosis.
In the beginning stages of melanin production, the skin has very little melanin or radiation protection capabilities. As a result, UVA radiation is not blocked by melanin pigments and, due to its longer wavelength, penetrates the skin deeper than UVB, causing damage to the corium. Damage to this layer of the epidermis hastens aging and destruction of collagen and connective tissue. A UVA burn can be much more damaging because it is not felt due to its deep penetration.
In order for the pigmentation process to be effective, melanin granules must be oxidized or darkened, which requires a high dose of long-wave UVA. Consequently, exposure to UVB radiation functions to create melanin pigment, while UVA exposure ensures the oxidation of the pigment. Together, a the proper combination of UV exposure operates to create a light-protection mechanism.
It is well recognized that to obtain the desired uniform tan, a person's facial region often requires the application of more intense radiation than the body region. This is due to the higher levels of melanin pigment present in the face, resulting from a more frequent exposure to the sun than the body. Prior attempts at designing a tanning chamber which provides a more uniform tan have included a lamp assembly which utilizes separate and distinct bulbs in the facial region. More specifically, higher intensity metal halide bulbs are positioned in the facial region and lower intensity bulbs extend over the body.
U.S. Pat. No. 5,557,112 to Csoknyai et al. discloses a fluorescent lamp having distinct and adjacent first and second zones along its length with different ultraviolet radiation characteristics. The first zone of the lamp has a first fluorescent coating applied to the inner surface of the tube for producing ultraviolet radiation having desired radiation characteristics. The second zone of the lamp has a second fluorescent coating applied to the tube for producing ultraviolet radiation having radiation characteristics which are different from those produced in the first zone.
Although these prior attempts may contribute to a more uniform tanning effect, they are more complicated to fabricate and maintain and are relatively expensive. This is especially true when the lamp is used in an application that requires more than two regions of varying intensity.
The patent literature also includes disclosures concerning tubular lamp assemblies that include constricted portions or grooves. See e.g., U.S. Pat. No. 2,916,645 to Lemmers et al.; U.S. Pat. No. 3,129,085 to Olsen et al.; U.S. Pat. No. 4,825,125 to Lagushenko et al; U.S. Pat. No. 3,988,633 to Shugan et al.; and Des. 198,268. The prior art patent disclosures also teach conventional systems and processes for forming such constricted portions and/or grooves in tubular lamps.
There is a continuing need for discharge lamps for use in applications such as tanning that provide enhanced lamp performance and/or energy delivery.